The invention concerns a cable, in particular an underwater cable, with a cable core having at least one conductor, and an outer sheath.
Underwater cables (so-called submarine cables) must be observed during laying, for inspection purposes and for tracing any defects. This takes place under water with remote-controlled cameras. The pictures taken by the cameras under water, in particular at great depths, often allow the underwater cable to be made out only with difficulty, in particular whenever it has a customary black or dark outer sheath. This makes it difficult in particular to locate defective underwater cables.
Setting out from the above situation, the invention is based on the object of providing a cable, in particular an underwater cable (submarine cable), which can be made out well under water, even at great depths.
A cable serving to achieve this object, in particular an underwater cable or submarine cable, has the features of claim 1. At least one externally visible marking of a different color on the outer sheath makes the cable more easily visible, in particular in the underwater area. The underwater cable according to the invention can be made out more easily on camera pictures, because the marking of a different color provides the outer sheath with greater contrast.
The marking can be formed in a wide variety of ways. The marking preferably consists of one or more strips or lines extending continuously in the longitudinal direction of the outer sheath of the cable and preferably extending spirally around the cable. The marking comprising one or more spiral longitudinal strips or longitudinal lines on the outer sheath has the effect that the marking is always visible, irrespective of from which side the cable is viewed. Since submarine cables turn about their longitudinal axis during laying, the longitudinal strips or longitudinal lines likewise running spirally around the longitudinal axis of the submarine cable represent a marking that is virtually always visible.
It is alternatively also conceivable to form the marking by transverse strips or transverse lines running in a cross-sectional direction around the cable. These are then virtually endless, colored rings around the outer sheath. They are also always visible, irrespective of any turning of the cable. Like the abovementioned longitudinal lines or longitudinal strips extending spirally around the cable, the peripheral transverse strips or transverse lines have the advantage that turning of the submarine cable during laying does not become visible and as a result does not disturb the viewer.
It is likewise conceivable to form the marking from straight longitudinal strips or longitudinal lines. In order that a straight longitudinal strip or longitudinal line is always visible in each case, a corresponding number of longitudinal strips or longitudinal lines are arranged evenly distributed on the circumference of the outer sheath. The longitudinal strips or longitudinal lines or transverse strips or transverse lines can also be produced from at least one series of two-dimensional formations following one another at intervals. The two-dimensional formations may have any desired base areas, and in particular be round, elliptical, square or rectangular. Similarly, the intervals between the two-dimensional formations may be as desired.
Finally, it is also conceivable to provide the entire outer sheath with a marking comprising dots of any desired shape. In this case, the dots are arranged in a uniform grid, which preferably extends over the entire circumference of the outer sheath. Such a grid also has the advantage that the marking is always visible and turns of the submarine cable during laying do not become evident and do not in this case detract from the observation of laying.
Any type of marking can be formed by a dye sprayed or printed onto the outer sheath after it has been produced. For this purpose, a dye which is permanently resistant to sea water is used. It is also conceivable, after applying the dye forming the marking, to provide the entire outer sheath with a transparent protective layer, which also covers the colored marking.
It is also possible to form the marking from a plastic of a different color during the production of the outer sheath. The outer sheath is then made up of differently colored plastic materials. For example, this can be achieved by coextrusion of the outer sheath or by sintering the plastic of a different color onto the surface of the outer sheath. The types of marking mentioned then have virtually the same sea-water resistance as the outer sheath.
According to a preferred development of the invention, the respective marking has a lighter color than the outer sheath. It is also advantageous if the lighter color of the marking has fluorescent properties. As a result, the marking of the submarine cable becomes visible even at great depths if searchlights of an underwater camera shine on it.
In the case of submarine cables with a usually black outer sheath, a yellow color, in particular a fluorescent yellow color, which offers easily visible contrast together with the black color of the outer sheath, is preferably chosen for the lighter color of the marking.
The marking may also be formed by mixing color particles or color pigments in with the raw material of the plastic for forming the outer sheath. Such an outer sheath then has an essentially regular distribution of colored locations, in particular small dots. The embedding of the color particles or color pigments in the plastic material for forming the outer sheath ensures a permanent bonding of the marking to the submarine cable.
In an alternative development of the submarine cable according to the invention, the marking is formed by a netting applied to the outer sheath. The netting surrounds the entire outer sheath and extends uninterruptedly in the longitudinal direction of the submarine cable. The netting produces on the outside of the outer sheath of the submarine cable peripheral transverse strands and rectilinear longitudinal strands with preferably a round cross section, although other cross sections, for example square, are also conceivable. If the netting is of a different color, the crossing longitudinal and transverse strands form the marking.